Thermoplastic polyester resins are widely used in the manufacture of various kinds of constructional materials due to their excellent mechanical strength characteristics, such as tensile strength, tear strength, impact resilience, freeze resistance, and flex resistance.
Because of their excellent mechanical strength characteristics, these resins are being used for components exposed to severe environmental conditions. However, under such sever environmental conditions thermoplastic polyesters tend to exhibit poor resistance to hydrolysis. And, thermoplastic polyesters usually do not offer adequate impact shock resistance when exposed to low temperature environments. There have been various attempts to improve or modify thermoplastic polyesters so as to overcome their inadequate resistance to hydrolysis and/or impact shock. These prior attempts usually include compounding polyester with other resins whose physical attributes overcome such disadvantages, or chemical modification of the polyester.
One attempt to improve the physical attributes of polyester in extreme environmental conditions involves compounding polyester with a more "elastic" resin (e.g., so-called elastic polymer loading), typical examples of which include SBR, BN and olefin elastomers. There have also been other attempts involving compounding of polyester with a resin having enhanced interfacial bonding with the polyester matrix. For example, it has been proposed in Japan Published Application Nos. 61-60744 and 61-60756 to introduce a glycidyl group into an olefin polymer for use as a modifier resin in a polyester resin matrix. Furthermore, Japan Patent Publication No. 61-42561 suggests that a carboxylic group may be introduced into an olefin polymer so as to improve its bonding capability with a polyester matrix. However, these prior attempts have not been successful due principally to the inadequate interfacial reactivity that is provided by means of the modifier resins.
Attempts to improve polyester resin characteristics through chemical modification have typically focussed upon the intramolecular introduction of an elastic segment into the polyester chain. However, such a technique is disadvantageous since intramolecular plasticization usually occurs with the result that the intrinsic mechanical strength characteristics of the resin are significantly sacrificed.
The present invention is therefore directed towards novel polyester resins which overcome the disadvantages of the prior attempts at achieving improved resin performance in extreme environmental conditions. According to the present invention, specific soft siloxane segments are introduced into the polyester polymer through covalent linkage. The resulting polyester copolymer exhibits good resistance to impact shock and to hydrolysis without any loss of the inherent advantageous properties of the base polyester resin.